Neptune has been directly explored by one space probe, Voyager 2, in 1989. As of 2024, there are no confirmed future missions to visit the Neptunian system, although a tentative Chinese mission has been planned for launch in 2024. NASA, ESA, and independent academic groups have proposed future scientific missions to visit Neptune. Some mission plans are still active, while others have been abandoned or put on hold.

Voyager 2 is a space probe launched by NASA on August 20, 1977, as a part of the Voyager program. It was launched on a trajectory toward the gas giants Jupiter and Saturn and enabled further encounters with the ice giants Uranus and Neptune. It remains the only spacecraft to have visited either of the ice giant planets, and was the third of five spacecraft to achieve Solar escape velocity, which will allow it to leave the Solar System. It has been sending scientific data to Earth for 46 years, 8 months, 23 days, making it the oldest active space probe. Launched 16 days before its twin Voyager 1, the primary mission of the spacecraft was to study the outer planets and its extended mission is to study interstellar space beyond the Sun's heliosphere.